Project Summary Mosquitoes are well recognized as the most important arthropod vectors of disease-causing pathogens. This is because most species must feed on vertebrate blood as adult females to reproduce. In turn, consumption of multiple blood meals enables pathogen transmission between hosts while vector abundance influences transmission risks. Thus, approaches that disrupt pathogen transmission and/or reduce vector populations are both strategies for disease control. Mosquitoes host microbes in their digestive tract that collectively form a gut microbiota. This application is a renewal request to continue our work on the essential role of the gut microbiota in mosquito development. Our current award focuses on Aedes aegypti, which is a major vector of several human diseases. Our studies to date indicate that microbe- induced gut hypoxia functions as a growth signal, and that transduction of this signal in mosquito larvae requires hypoxia-induced transcription factors (HIFs). Results further indicate that HIF signaling activates several processes with essential roles in nutrient acquisition, growth and metabolism. The overall goal of this proposal is to unravel the molecular mechanisms that connect microbe-induced gut hypoxia and HIF signaling to the nutrients and signaling pathways that regulate growth. Proposed studies have the potential for transformative impacts on understanding the role of the gut microbiota in development of most if not all vector mosquito species. Proposed Specific Aims are to: 1. Identify HIF target genes in Ae. aegypti. 2. Characterize Ae. aegypti HIF-? isoforms. 3. Analyze the role of HIF signaling in lipogenesis and midgut growth. 4. Assess the role of the gut microbiota as nutrient source for mosquito development. Expected outcomes will identify molecular targets for disrupting mosquito development and factors that could improve mosquito rearing for control programs. Results will also guide understanding of how diet and the gut microbiota regulate growth of all mosquito species.